Chicken pox herpes zoster
dr hadeel fadhil FIBMS
Chicken pox (varicella) is an acute, generalized viral disease with sudden oncet of slight fever , skin eruption that is maculopapular for afew hours , vesicular for 3-4 days & leaves a granular scab .the vesicles tend to be more on coverd than exposed parts of the body . Lesions may appear on the scalp , high in axilla , on mucous membranes of the mouth & upper respiratory & on the conjunctivae , they tend to occur in areas of irritation , such as sunburn or diaper rash .
**mild a typical& inapparent infections occur especially in adults , the fever may be sever.
The case fatality rate is lower for children than for adults . One out every 100000 children with varicella , compared with 1 out of every 5000 adults . Prior to the availability of effective viral therapies , the fatality rate was up to 30% , but it is likely lower now .
Complications
* pneumonia ( viral and bacterial )
* secondary bacterial infections
*hemorrhagic complications
* encephalitis
Infection early in pregnancy may be associated with congenital varicella syndrome in 0.7% of cases , and infection occurring at 13-20 weeks of gestation may be associated with 2% risk .
Herpes zoster ( shingles )
Is a local manifestation of reactivationof latent varicella infection in the dorsal root ganglia . Vesicles with an arythematous base are restricted to skin areas applied by sensory nerves of a single or associated group of dorsal root ganglia .
Lesions may appear in croups in irregular fashion along nerve pathways , are usually unilateral, deeper seated and more closely aggregated than those of chickenpox .
Sever pain and parasthesia are common .
Increase risk of HZ occur in children treated for malignancy , HIV , on immunsupprutave RX , malignancy .
Infectious agent
Human (alpha) herpesvirus 3 ( varicella zoster virus ) . A member of the herpesvirus group.
Occurrence
World wide , most frequantly in winter & early spring .
Zoster occure more commonly in older people
Reservoir :humans .
Mode of transmission
-person to person by direct contact
- airborne spread of vesicle fluid or secretions of the respiratory tract of chickenpox cases or of vesicle fluid of patient with HZ , indirectly through articles freshly soiled by discharges from vesicles of mucous membranes of infected people .
Chickenpox is one of the most readily communicable of diseases , especially in the early stages of the eruption , zoster has much lower rate of transmission .
Susceptible have about 80-90% risk of infection after household exposure to varicella .
Incubation period
From 2-3 weeks , commonely 14-16 days .
Period of communicability
As long as 5 but usually 1-2 days before onset of rash, and continuing until all lesions are crusted ( usually about 5 days).
Patient with zoster may be source of infection for a week after the appearance of their vesiculopustular lesion .
Susceptible individuals should be considered to be infectious 10-21 days following exposure.
Susceptibility & resistance
Susceptibility to chickenpox is universal among those not previously infected , ordinarily a more sever disease of adults than of children .
Infection usually confers long immunity , second attacks are rare but have been documented in immunocompetent persons , subclinical reinfection is common .
Viral infection remains latent, the disease may recur years later as herpes zoster in about 15% of older adults, & some time in children .
Methods of control
A- preventive measures :
1- live attenuated varicella virus vaccin .
A single 0.5 ml Sc dose is recommended for routine immunization of children up 12 yr of age who have not had varicella .
Varicella vaccine is recommended for susceptible persons more than 13 yr .
Priority groups for adult immunization include:
-Person who have close contact with persons at high risk for serious complications .
Persons who live or work in enviroments where transmission of VZV is likely
(Teachers of young children , day care employees & residents & staff members in institutional setting)
- persons who live & work in environments where transmission can occur ( college students , military personnel )
- non pregnant women of childbearing age , adolescents &adults living in household with children & international travelers .
**Persons more than 13 yr old require 2 dose of vaccine 4-8 weeks apart .
***Mild varicella- like rash at the site of injection or at distant sites occur in about 2%-4% of children & about 5% of adults.
**The duration of immunity is unknown , but antibodies have persisted for at least 10 yr .
2- protect high risk individuals who cannot be immunized , such as nonimmune neonates & immunodeficient, from exposure by immunizing household or other close contacts .